The present invention relates to an autoinductive electromagnetic pump and an autoinductive direct converter. Electromagnetic pumps have been particularly studied for their use in the nuclear field and particularly for the circulation of liquid Sodium in the circuits of the breeding nuclear reactors.
Such components may be arranged in any circuit containing an electrically conducting liquid metal and consistent with an amagnetic material necessary for making the conduits.
The operation principle of electromagnetic pumps is based on the action of Laplace force generated in a conductor having an electric current therethrough, by a magnetic field.
In said pumps the conductor consists of the fluid itself subject to an action tending to move it perpendicular to the plane containing the magnetic flow lines and the current line.
The best operation conditions are obtained when the directions of the magnetic field, electric current and sliding are perpendicular two by two.
Such operation principle was used in embodying various types of electromagnetic pumps, each of them with particular features which will be considered individually.
The simplest application of the above principle is represented by the conductive electromagnetic pumps at single-phase alternate current. The conduit containing Sodium is arranged in the air core of a magnetic circuit, where a magnetic field perpendicular to the slide direction of the fluid is generated. A current is made to circulate from one side to the other of the circuit by means of two electrodes connected to an alternate voltage supply system. The driving power is produced by the interaction between an alternate current, delivered by the secondary winding of a transformer, and an alternate magnetic field generated by the secondary winding of a second transformer. The primary windings of said two systems are connected to a same supply, so as to synchronize the current and magnetic field. In this type of pump a particular care is to be taken in making the pump supports for reducing vibrations and noise effects due to the use of a single-phase alternate current. For cooling said component, the heat dissipation due to the natural convection is sufficient, provided that the Sodium temperature does not exceed 650.degree. C.
A second type of electromagnetic pump for conducting fluids is represented by the induction electromagnetic pump.
In induction flat pumps, the conduit for the conducting fluid is of reatangular section and the input is in a three-phase alternate current. The stator windings generate perpendicular to the conduit a sliding sinusoidal magnetic field which induces currents into the liquid Sodium. The electromagnetic forces generated by the interaction between the magnetic field and the induced currents make the fluid move.
The embodiment of said components is very simple, in fact they advantageously do not include electrodes or current circulation and therefore they may be easily disassembled and removed, with the conduit kept welded to the circuit. These pumps are used with Sodium up to 600.degree. C., but their operation improves with the decrease of temperature.
A third type of electromagnetic pump is represented by the induction annular pumps. Said pumps have such a shape that the fluid ciculates within the annular space comprised between two concentric pipes, while the three-phase stator, arranged around the outer pipe, generates radially a sliding magnetic field. That induces currents into the liquid Sodium, which reclose circularly on themselves, and the force generated by the interaction between current and magnetic field tends to make the fluid move.
Said pumps, for their particular structural arrangement, are more advisable than others for obtaining pumping units in position to offer deliveries up to some thousands of m.sup.3 /h with a head of 10.div.15 bars.
The above mentioned types of electromagnetic pumps for conducting liquids have the following common advantages:
simple operation, that is simple adjustment of the delivery; in fact, it is sufficient to change the supply voltage for varying the Sodium flow; PA1 tighness assured by the absence of penetration into the conduit, and of movable parts; PA1 minimum maintenance owing to said absence of movable parts; PA1 no problem of lubrication; PA1 no need of any covering inert gas, as the conduit is perfectly tight; PA1 operation with liquid metals up to 600.degree. C. and in some cases to 800.degree. C; PA1 mounting of the circuit in situ on the conduit by welding.
The common inconvenience of the above mentioned various types of solution is that large deliveries and remarkable heads are not available simultaneously. That restricts the range of use on primary or secondary circuits of large reactors.